1 Field of the Invention
The present invention relates to a radio frequency air float bar for use in positioning, drying or curing of a continuous planar flexible material such as a web, printed web, news print, film material, or plastic sheet. The present invention more particularly, pertains to a radio frequency air float bar whose pressure pad area includes a radio frequency radiator to enhance accelerated heating of a web material to cause solvent evaporation, drying or curing. Radio frequency energy in combination with columns of heated air impinging upon the web surface provides for concentrated heating of the web material thereby providing subsequent rapid evaporation, drying or curing from the surface of the material.
2. Description of the Prior Art
Demand for increased production volume and production speed of web material in dryers has caused the printing industry to increase web speed on their printing lines. Typically this speed-up requirement resulting in the dryer being inadequate in drying the web, because the web did not remain in the dryer adjacent to a series of air bars for a sufficient length of time to dry the web because of the increased web speed. The solution for adequate drying was to either replace the entire dryer with a longer dryer, or to add additional drying zones in series with a first dryer zone. This, of course, is expensive and often times not feasible due to a shortage of physical floor space.
The present invention overcomes the disadvantages of the prior art dryers by providing a radio frequency air float bar to replace existing air float bars in web dryers. In addition to air flow of dry air from the Coanda air flow slots at the upper and outer extremities of the air float bar, a radio frequency radiator is located between the Coanda air flow slots, and transmits radio frequency electromagnetic radiation waves to the traversing web. The traversing web drying is accomplished by impingement of a combination of both heated Coanda air flow and radio frequency electromagnetic energy radiation. The combined concentration of heat from the Coanda air flow and the radio frequency electromagnetic energy radiation from the radio frequency radiator is of a sufficient magnitude which allows the web to dry at a higher speed than normal prior art speed.
U.S. Pat. No. 4,638,571, issued to Cook, teaches the use of radio frequency energy in combination with an air dryer bar. However, Cook produces an electromagnetic field between electrodes located in a plane which is parallel to the traveling web of material. The result is uneven distribution of energy across the width of the traveling web. This technique is also inefficient in the transfer of maximum energy.